This application claims the benefits of Japanese Application Nos. 10-227525 and 11-208150 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a sealed rolling bearing having a design for preventing water, or the like, from invading from outside into the bearing space.
2. Related Background Art
As a bearing to be used in an environment in which it may be splashed with fluid including water, such as a roll neck bearing of a rolling mill in steel mill equipment, a sealed rolling bearing provided with a sealing device as proposed in Japanese Patent Publication No. 60-14933, No. 61-12130, or the like, is used.
A four-row tapered roller bearing provided with a seal for hermetically sealing is shown in FIG. 30 as one example of the sealed rolling bearing. Note that FIG. 30 shows an upper half of the longitudinal cross-section of the bearing excluding the shaft thereof.
The sealed roller bearing shown in the same Figure is provided with a large number of rollers 4, 4, . . . which are supported by a four-row retainer to be rotatable, in a bearing space S between outer races 1, 1, 2 and inner races 3, 3, so as to enable the rotation of the inner races 3, 3 with respect to the outer races 1, 1, 2. Further, seal holders 7, 7 are disposed at the outside ends of the outer races 1, 1 in the axial direction thereof, so as to support seals 8, 8, whereby elastic lips 8a, 8a of the seals 8, 8 are brought into contact with the outer peripheral surfaces of the inner races 3, 3 at the outside ends in the axial direction thereof. Consequently, it is possible to retain a lubricating member inside the bearing space, and to prevent fluid such as water from invading into the bearing space S.
FIG. 31 is a view for illustrating the shape of an intermediate seal 019 which is retained on the inner surface of a portion in which the inner races 3, 3 are in contact with each other. This intermediate seal 019 is arranged to prevent water, or the like, from invading into the bearing space S chiefly when a roll is attached or detached.
FIG. 22 shows another example 9xe2x80x2 of the intermediate seal which has been conventionally used. This intermediate seal 019xe2x80x2 has lip portions 019a, 019b which are brought into linear contact with the bottom surfaces 3b, 3b of a recess formed by the facing portions of the inner races 3, 3. The contact surface pressure is increased by this linear contact, thereby sealing the inside and the outside of the bearing.
The conventional hermetically sealed rolling bearing mentioned above can not satisfactorily prevent the invasion of water or the like, under a severe environment with drastic change in temperature.
For example, when the sealed rolling bearing shown in FIG. 30 is used as a roll neck bearing for a rolling mill in steel mill equipment, the number of rotations of the roll which is supported by this hermetically sealed rolling bearing is frequently changed. More specifically, a high-speed rotation, low idling rotation, and a halt are repeated for the roll, and the temperature inside the sealed rolling bearing changes depending on each of the conditions. For this reason, expansion and contraction of the air or the like in the bearing space are repeated, the internal air which is expanded upon the increase in the temperature escapes from the elastic seals 8, 8 on the end surfaces, and the pressure inside the sealed rolling bearing becomes negative when the temperature is decreased for the second time.
The value of this negative pressure becomes larger and is maintained longer when the temperature inside the bearing space S which has been high becomes lower (or a difference of the temperature is larger), that is, the number of rotations of the roll which has been rotating at a high speed becomes smaller (a difference of rotation is larger). These conditions are shown in FIG. 28A, FIG. 28B and FIG. 28C. These views respectively show the number of rotations of the roll, the temperature in the bearing (the temperature inside the bearing space S), and the internal pressure of the bearing (the pressure in the bearing space S), with respect to time (along the abscissa) in that order.
Also, when the internal temperature is 100xc2x0 C. or higher with a little water existing inside, this water is expanded as vapor, and a large negative pressure is generated when the temperature decreases. This negative pressure accelerates abrasion of the elastic seal lips of the seals 8, 8, to degrade the function of the seals 8, 8, which is a great cause of water invasion from the seals 8, 8.
As described above, it is confirmed that when a great negative pressure is generated in the bearing space S, the greater the negative pressure is, the easier the invasion of external fluid such as water through the lip portion 8a of the elastic seal becomes. More specifically, as clearly seen from FIG. 29, the greater the negative pressure is (more to the left of the abscissa in the figure), the easier the flow of water into the sealed bearing becomes, thereby increasing an amount of the mixed water. The easier inflow of water means a degraded sealing function. In addition, the water inflow and the degraded sealing function accelerate deterioration of the lubricant in the bearing space S to degrade the bearing performance, thereby causing early damage or early peeling-off.
Accordingly, an object of the present invention is to provide a hermetically sealed rolling bearing capable of preventing deterioration of a lubricant due to the inflow of water which may be caused by the negative pressure in the bearing space, thereby preventing deterioration of the bearing performance, early damage, early peeling-off, etc.
In order to achieve the above object, there is provided a hermetically sealed rolling bearing in which rolling members are disposed in a bearing space formed between an outer race and an inner race to rotate the outer race and the inner race relatively to each other, and side seal members are disposed at the ends of the bearing space in the axial direction thereof while a bore seal member is disposed on the side of the inner race, thereby sealing the bearing space, characterized in that: there is provided vent means on the side of the inner race for approximating a fluid pressure in the bearing space to an outside fluid pressure when the state of the fluid in the bearing space and the state of the outside fluid becomes a predetermined relationship.
Here, in the sealed rolling bearing according to the present invention, there is provided the vent means on the inner race side to approximate the fluid pressure in the bearing space to the fluid pressure outside when the state of the fluid in the bearing space and the state of the fluid outside reaches a predetermined relationship. Thus, even if, for example, the heated sealed rolling bearing is cooled, the fluid pressure in the bearing space is approximated to the fluid pressure outside so as not to pull the water or the like into the bearing space. Also according to an especially preferred mode of the present invention, the vent mechanism is disposed at a position which is hardly exposed to external water or the like so that the above-mentioned function can be realized in a simpler and a more secure manner.